December 10, 2019
by Zeeshan Sheikh, Dip.Dh, BDS, MSc, PhD; Nader Hamdan, BDS, MSc, MDent (Perio); Haider Al-Waeli, BDS, MSc, PhD; Michael Glogauer, DDS, PhD, Dip.Perio
Single dental implant placement immediately post extraction for the rehabilitation of esthetic areas is a predictable procedure characterized by high survival rates in the short and long terms.1,2 However, this is challenging to achieve as the restoration is required to mimic the natural profile in near perfect symmetry along with the contralateral tooth present.2 To attain an effective esthetic outcome with a single implant supported restoration in the anterior region, it is imperative to preserve and maintain intact the bone anatomy, as well as the overlying soft tissues.2,3 Availability of sufficient alveolar ridge height and bone volume is crucial for attaining the long-term clinical success of dental implants.4 After loss, if teeth are not replaced immediately, bone volume and height decreases rapidly by active resorption.5,6 Alveolar bone loss of around 1.5-2 mm vertically and up to 3.8 mm horizontally takes place within the first six months after tooth loss.7,8 If no treatment is provided, then bone loss continues to occur and 60% of total ridge volume can be lost in the first three years.9,10 The greatest amount of bone loss occurs on the buccal aspect, which is related to a thinner bone wall composed of large amounts of bundle bone primarily vascularized by the periodontal tooth membrane and particularly susceptible to surgical trauma and resorption (Fig. 1).11,13
The loss of bone tissue in the vertical and horizontal dimensions leads to great challenges towards successful placement of dental implants and adversely affects the esthetic outcome, implant positioning and osseointegration.14 This is even more critical in the anterior regions where these changes directly influence esthetic outcomes.15 Several surgical techniques have been proposed and investigated to try and limit the physiologic bone resorption that follows tooth extraction in the anterior region. Some of these techniques are alveolar socket preservation,16 soft-tissue grafts, implant placement directly after extraction, positioning of the implant on the palatal/lingual wall, preserving the buccal wall contact,1 performing the surgery using the flapless technique to maintain vascularization1, and guided bone regeneration (GBR) with membranes18-23 and/or with grafting materials.18-24 Although these techniques work to a certain extent, they are by no means ideal and none have been shown to completely eliminate the challenge of buccal plate resorption post extraction of teeth (Fig. 2).25
An alternative to the conventional techniques is called ‘‘socket shield’’ technique (SST), which was first described by Hurzeler et al.15 The concept of this technique is to preserve the periodontal ligament (PDL) associated with the buccal portion of the root and the vascular supply. This is an attempt to avoid the buccal bone wall resorption that usually follows conventional tooth extraction.15,26 Better esthetic outcomes are expected to be achieved by maintaining the PDL and the blood vessels associated with it by preventing physiologic bone resorption of the buccal bone and contraction of the overlying soft tissues.15,26
This “Partial Extraction Therapy” (PET) (Fig. 3) involves the sectioning and removal of the crown of the non-restorable tooth, leaving only the root, which is then sectioned into two parts, mesiodistally.15,26 Following this, the palatal root portion is then carefully extracted while ensuring not to damage or mobilize the buccal portion of the root.15 The buccal portion of the root is reduced in thickness (to assume a concave shape similar to the profile of the bone crest) and in height (up to 1mm above the bone ridge) in contact with the buccal bone.15 Following this, an immediate dental implant is placed, palatally to the remaining buccal root portion.15,26 Gluckman et al, suggest that the gap between the implant and the buccal portion of the root if present, should always be grafted with particulate bone graft material.27,28 However, Siormpas and Mitsias suggest that it is not necessary;29,30 because the essence of this method consists of preserving the periodontal ligament and hence the associated vascular contribution.29,30
Figure 3. Partial extraction therapy (P.E.T.): A & B. Pre-operative photographs showing a maxillary central incisor planned for extraction C. Fixed permanent restoration (PFM crown) was separated from the root and kept for subsequent use as a temporary crown D. Remaining natural root sectioned in a mesio-distal direction E. Palatal portion of the sectioned root extracted leaving a thin shell of the original root intact and still attached to the buccal bundle bone F-H. An immediate dental implant carefully inserted into proper position palatal to the remaining root shell. (Adapted from Sheikh et al. Post-extraction Socket and Ridge Preservation. Oral Health Journal. 2018)
Meticulous presurgical planning is mandatory for PET therapy to be successful. The technique is indicated for the anterior areas of both jaws for teeth that cannot be restored.31 However, the technique cannot be applied to teeth with present periodontal disease (present or past), to teeth with mobility or widening of the PDL, to teeth that have vertical root fractures or horizontal fractures below bone level, or to teeth with that exhibit internal/external resorptions.31
How Stable/Predictable Is The Partial Extraction Therapy?
Since the presentation of PET technique in 2010 by Hurzeler,15 dentists have started to incorporate and implement this concept into their treatments for patients. The issue of having a standardized PET treatment has been addressed by Gluckman and his colleagues by suggesting their standard treatment approach for the Socket Shield Technique.32 Since, many have tried this procedure with different ranges of success.33-40 Gluckman in a four-year follow-up study found 96% of socket shield therapy (SST) sites had no complications which is similar to immediately placed implants.41 Han reported 100% success after a one-year follow-up with 40 SST procedures performed on 30 patients. Zhu had 100% success on nine patient’s follow-up between a 12-48 months.42 Bramanti compared SST to conventional implant placement and followed up his cases for three years. Bramanti compared implant survival, marginal bone level and the pink aesthetic score between the two comparison groups and found the SST was superior in all three categories.40
This initial reported success of the PET has led to the discussion that how much root needs to be left in the extraction socket to achieve optimal success. Two studies looked at the length and the width of the remaining root and compared this to the overall effect on bone preservation. Calvo-Guirado compared the location of the root segment whether it was in the coronal, middle, or apical third of the socket. He found that within the limitations of his study the coronal third was the most effective at preventing buccal bone resorption.43 This is biologically plausible as the buccal plate of bone gets wider in the more apical direction. Thus, it could have its own blood supply and be able to survive the trauma from a tooth extraction apically. Tan compared the width of the root shield left behind. He compared different root shields widths ranging from 0.5-1.5 mm and found that bone resorption decreased with increased root width.44
Limitations of the Partial Extraction Therapy
There have been reports of complications with employing PET. Gluckman reported that nearly 20% of the implants placed with PET had some form of complication.41 The most common being internal/ external exposure of the root shield. However, majority of these complications were managed successfully.41 A systematic review done in 2017 found that 82.86% of the four animal histological studies reviewed had complications and 24% of implants from 21 studies on human cases had complications.31 The most common complications observed were root shield exposure and loss of buccal bone. The systematic review concluded that it is hard to predict the long-term outcomes of PET treatments with the current available level of weak evidence. Gluckman and Schwimer have attempted to address the exposure of root shield by beveling the root shield to be below the crest of the bone and to provide more space for tissue development around the dental implant.28,45 However, further well designed and extensive clinical studies must be performed to prove this as an effective and predictable option.
PET is a unique treatment alternative that requires one surgical procedure thus reducing patient morbidity, as well as, reducing overall treatment time and cost associated with treatment. The disadvantage is that it cannot be performed for every tooth since multiple criteria needs to be met for PET to be considered, such as tooth mobility, complete absence of endodontic apical pathology, and/or narrow thin roots. Since there are only a few clinical studies available on PET, little is known about the possible failures and/or complications associated with this technique. Although PET therapy shows great promise of helping to preserve the buccal plate following teeth extraction, it requires further study and review (long-term).
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About the Authors
Dr. Zeeshan Sheikh trained as a dental clinician & a biomaterials scientist from Baqai University, Queen Mary University of London, McGill University, U of T and Mt. Sinai Hospital. He is a Surgical Resident at Dalhousie University in the Periodontics and Implant Surgery specialty program.
Dr. Nader Hamdan is an Assistant Professor/Director of the Graduate Periodontics Program, Faculty of Dentistry at Dalhousie University and a member of the American Academy of Periodontology, the Canadian Academy of Periodontology, the Atlantic Society of Periodontists, and the Steering Committee of the Network for Canadian Oral Health Research (NCOHR).
Dr. Haider Al-Waeli was trained as a clinician scientist from Baghdad University, Jordan University of Science & Technology, and McGill University. He worked as a clinician academician in Jordan, Malaysia and Canada. He is a Surgical Resident at Dalhousie University in the Periodontics and Implant Surgery program.
Dr. Michael Glogauer is a Professor at U of T and Interim Head of Dental Oncology at Princess Margaret Hospital. He is currently focusing on using oral innate immune biomarkers to detect early stages of periodontal diseases through his role as Scientific Director at the Mt. Sinai Hospital’s Centre for Advanced Dental Research and Care. He is also a periodontist at OMGPerio.ca.